1. Field of the Invention
The present invention relates to a base station system, a data transmission method of a multicarrier CDMA/FDM hybrid system, and a mobile communication system using the same, and in particular to an improved base station system, data transmission method, and a mobile communication system using the same which are capable of increasing the number of mobile stations supported in a cell when using a multicarrier CDMA method by differently setting a modulation mode of a traffic signal in accordance with the number of the mobile stations in a cell.
2. Description of the Conventional Art
The multicarrier CDMA system and data transmission method is disclosed in the U.S. Pat. No. 5,521,937 entitled xe2x80x9cMulticarrier direct sequence spread system and methodxe2x80x9d. In the patent, the DSSS(Direct Sequence Spread Spectrum) in which the spectrum of a user data is spread using a PN(Pseudo noise) code is transmitted to various different frequency channels, a receiver receives the signals at each frequency channel and then combines the received signals for thereby demodulating it. In this mobile communication receiver, it is possible to obtain a combining gain and signal processing gain from the diversity of channel characteristics the frequency channels.
FIG. 1 illustrates a base station system supporting a K mobile stations and using four carrier waves in the mobile communication system using the multicarrier CDMA method.
In the drawings, reference numeral 102 represents an exchange, 104 represents a base station system, 106 represents a base station control apparatus, 108 represents a pilot signal modulation apparatus, 110 represents a paging signal modulation apparatus, 112-1 through 112-K represent traffic signal modulation apparatuses, 114-1 through 1144 represent combining units, 116-1 through 116-4 represent BPSK(Binary Phase Shift Keying) modulators, 118 represents a radio frequency(RF) combining unit, 120 represents an amplifier, and 122 represents an antenna.
The exchange 102 communicates with the base station control apparatus 106 in the base station 104. The base station control apparatus 106 controls the pilot up signal modulation apparatus using a CDMA/FDM(Frequency Division Multiplexing), the paging signal modulation apparatus 110 and the K number of the traffic signal modulation apparatuses 112-1 through 112-K.
The pilot signal modulation apparatus 108 outputs the first, second, third and fourth signals, which are the same pilot pseudo noise (PN) code.
The paging signal modulation apparatus 110 outputs the first, second, third and fourth paging signals, which are the same paging spread spectrum signals. Here, the paging spread spectrum signal is obtained by multiplying the paging information data bit inputted from the base station control apparatus and the paging PN code.
In the K-number of the traffic signal modulation apparatuses 112-1 through 112-K, four traffic spread spectrum signals are generated by multiplying the four user data bits and the traffic PN code in parallel, and four spread spectrum signals are output to first, second, third and fourth traffic signals.
The first through fourth combiners 114-1 through 114-4 sum the first through fourth pilot, paging, and the K number of the traffic signals, respectively.
The first through fourth BPSK modulators 116-1 through 1164 modulate the outputs of combiners 114-1 through 114-4 to the radio frequency using the frequencies f1, f2, f3. The RF(Radio Frequency) modulated by the first through fourth BPSK modulators 116-1 through 116-4 are combined by the RF combiner 118. In addition, the output from the RF combiner 118 is amplified by the amplifier 120 and is transmitted through the antenna 122.
When the frequency transmitted through the antenna 122 is received at a predetermined terminal, the terminal converts each spread spectrum signal received in a carrier frequency into a base band frequency. The codes allocated to the terminal are multiplied and despread. In addition, the above-described terminal combines the despread signals using a maximal-ratio combiner for thereby demodulating the user data.
Here, the pilot signal modulation apparatus 108 and the first through fourth BPSK modulators 116-1 through 1164 are the elements of the multicarrier pilot signal modulation apparatus. The paging signal modulation apparatus 110 and the first through fourth BPSK modulators 116-1 through 1164 are the elements of the multicarrier paging modulation apparatus. The traffic signal modulation apparatuses 112-1 through 112-K and the first through fourth BPSK modulators 116-1 through 116-4 are the elements of the multicarrier signal modulation apparatus.
In the mobile communication system of the multicarrier CDMA, the number of code chips per data bit is reduced by the number of the carriers compared to the mobile communication system of a single carrier CDMA using the identical bandwidth. In the cellular mobile phone system of the CDMA, orthogonal codes are used for distinguishing mobile stations at the link from the base station to the mobile station. The number of orthogonal codes is the same as the number of the code chips per data bit.
Therefore, the number of the codes for distinguishing the mobile stations which may be used for the mobile communication system of the multicarrier CDMA is reduced by times the number of the carriers compared to the single carrier mobile communication system using the identical bandwidth.
In the mobile communication system of the multicarrier CDMA using four carrier frequencies having the construction as shown in FIG. 1, the number of the code chips per data bit is reduced by xc2xc compared to the mobile communication system of the single carrier method.
Therefore, the number of the orthogonal codes which may be allocated to each mobile station is reduced by xc2xc as well. In the base station of the mobile communication system of the multicarrier method, in order to support the same number of the mobile stations as the number of the mobile stations which may be used in the base station of the mobile communication system using the single carrier method, the code allocated to each mobile station should be a code which is not orthogonal to each other. Namely, a quasi-orthogonal functions or a random sequence should be used instead of the orthogonal function for distinguishing the mobile stations. However, if the quasi-orthogonal function or the random sequence is used, since the interference between the mobile stations in the same cell is increased, the bit error rate is increased for thereby degrading the performance of the system.
Accordingly, it is an object of the present invention to provide a base station system and a data transmission method of a multicarrier CDMA/FDM hybrid system and a mobile communication system using the same which overcome the aforementioned problems encountered in the conventional art.
It is another object of the present invention to provide a base station system of a multicarrier CDMA, a data transmission method and a mobile communication system using the same which are capable of controlling a lot number of mobile stations by distinguishing the mobile stations using orthogonal codes at a link from a base station to a terminal of a cellular system using the multicarrier CDMA and removing interference from signals transmitted to the other mobile stations in the same cell.
In order to achieve the above objects, there is provided a base station system which includes a base station control apparatus connecting with an exchange, a pilot signal modulation apparatus for generating a spread spectrum modulated pilot signal as many as the number of carriers in accordance with a control of the base station control apparatus, a paging signal modulation apparatus for generating spread spectrum modulated paging signals as many as the number of carriers in accordance with a control of the base station control apparatus, a plurality of traffic signal modulation apparatuses, each of which generates spread spectrum modulated traffic signals as many as the number of carriers in accordance with a control of the base station control apparatus, a plurality of combiners provided as many as the number of the carriers for combining input signals from the modulation apparatuses, and a radio frequency transmission apparatus for modulating the outputs from the combiners into a radio frequency and transmitting the same, wherein said base station control apparatus determines the modulation mode in accordance with the number of mobile stations in a cell, and the determined modulation mode is contained into the paging signal and then is transmitted, and the traffic signal modulation apparatus is controlled in accordance with the determined modulation mode, and wherein said traffic signal modulation apparatus symbol-repeats the user data bits for a predetermined time in accordance with the modulation mode determined by the base station control apparatus and modulates a plurality of carriers using a traffic spread spectrum signal obtained by multiplying the symbol-repeated user data bit with a data bit which is serial/parallel-converted as many as the carriers and the traffic pseudo noise code.
In order to achieve the above objects, there is provided a data transmission method for a mobile communication system using a multicarrier method which includes a first step for determining a modulation mode in accordance with the number of the mobile stations in a cell in the base station control apparatus, a second step for performing a spread spectrum modulation with respect to a paging information including the determined modulation mode, a pilot information and a traffic information as many as the number of the carriers, a third step for modulating the radio frequency signal including the spread spectrum modulated paging signal, the pilot signal and a plurality of traffic signal by each carrier and transmitting the same to the mobile station, a fourth step for detecting a code phase of the receiving signal and an information with respect to the carrier phase from the pilot signal received from the mobile station, and a fifth step for classifying the modulation mode used in the base station from the paging signal received by the mobile station and demodulating the received traffic signal using the detected phase information and the modulation mode, wherein traffic information modulation step, the user data bit is symbol-repeated for a predetermined times in accordance with the determined modulation mode, and a plurality of carriers are modulated using a traffic spread spectrum signal obtained by multiplying the serial/parallel converted data bit and the traffic pseudo noise code as many as the number of the carriers with respect to the symbol-repeated user data bits.
In order to achieve the above objects, there is provided a mobile communication system which includes a base station control means for determining a modulation mode in accordance with the number of mobile stations in a cell, for including the determined modulation mode into a paging signal and for controlling a spread spectrum modulation in accordance with the determined modulation mode, a pilot signal modulation means for generating a spread spectrum modulated pilot signal as many as the number of the carriers in accordance with a control of the base station control means, a paging signal modulation means for generating the spread spectrum modulated paging signal in accordance with a control of the base station control means, a traffic signal modulation means for symbol-repeating the user data bit for a predetermined times in accordance with the modulation mode determined by the base station control means and for generating traffic spread spectrum signal obtained by multiplying the symbol-repeated, serial/parallel converted data bits and the traffic pseudo noise code, a plurality of combining means provided at many as the carriers for combining the signals inputted from the modulation means, and a radio frequency transmission means for modulating the output signals from the combining means to the radio frequencies, and said mobile station comprising a pilot signal receiving means for detecting a code phase and a plurality of carrier phases of the signal transmitted from the base station, an information receiving means for demodulating the paging signal and the traffic signal received from the base station, and a mobile station control means for controlling the pilot signal receiving means and the information receiving means, detecting the modulation mode from the paging information demodulated by the information receiving means and demodulating the traffic signal using the detected phase information and the modulation mode.
Additional advantages, objects and other features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objects and advantages of the invention may be realized and attained as particularly pointed out in the appended claims as a result of the experiment compared to the conventional arts.